Iron-based steel is commonly used in a wide variety of applications. Nano-ferritic alloys and oxide-dispersion strengthened (ODS) steels are alloys having particles of an oxide material (e.g., yttria (Y2O3)) dispersed within the alloy. ODS steels have enhanced mechanical properties at high temperatures, yet maintain high thermal conductivity and low thermal expansion. The oxide material appears to slow degradation processes, such as recrystallization.
Historical fabrication methods generally employ powder metallurgy to mechanically disperse oxide particles within alloys. Thus, ODS steels are conventionally formed by mechanically alloying powders of the oxide material with the alloy in solid form. Such processes are time-consuming and labor-intensive, making ODS steels relatively expensive and difficult to make in large batches, which affects their limited application in industry. Furthermore, the directionality in microstructures formed during processing, such as rolling to form plates and foils, and extruding to form tubes, generally produces undesirable anisotropic mechanical properties.
The density difference between the oxide particles and the alloy typically prevents welding of ODS steels by conventional techniques such as fusion welding. When ODS steel is melted to form a weld joint, the particles of the oxide material separate from the alloy by density. For example, Y2O3 has a density of about 5.0 g/cm3, so Y2O3 particles tend to float to the top of molten steel (which has a density from about 7.75 g/cm3 to about 8.05 g/cm3). ODS steel may be welded by more difficult and expensive techniques, such as magnetic-pulse welding, friction-stir welding, or pressure-resistance welding. Such techniques, which are expensive and experimental, must generally be carefully controlled to limit or prevent melting of the ODS steel because melting of the ODS steel may lead to separation of the oxide material from the bulk alloy.